This invention relates to systems for automatic or computer-controlled manipulation of sheet material during processing, e.g., fabric or other limp material to be assembled at a sewing station.
During the construction of a useful item from raw stock of flat goods (e.g., cloth, paper, plastic, and film), it is often necessary to precisely position and guide the flat goods through a work station. Typical work stations perform assembly operations such as joining, cutting or folding. For example, such work stations can be equipped with sewing machines for joining multiple layers of limp fabric.
Conventionally, the positioning and guiding of the fabric-to-be-joined is accomplished by skilled human operators. The operators manually feed or advance the fabric-to-be-joined through the stitch forming mechanism of the sewing machine along predetermined seam trajectories on the fabric. The resultant seams can be straight or curved, or a combination of both as is often required in the assembly of fabric panels to form articles of clothing, for example. Typically, the fabric-to-be-joined must be precisely positioned and accurately directed to the sewing head to achieve the desired seam. The human operator must therefore function not only as a "manipulator" of the fabric but also as a real-time "sensing and feedback medium", making small adjustments, e.g., in orientation, fit-up and seam trajectory, to obtain quality finished goods. The adjustments are required, for example, due to variations in seam type, geometry, location and fit-up.
One drawback of this technique is that it is labor intensive; that is, a large portion of the cost for manufacture is attributable to manual labor. To reduce labor cost, automated or computer-controlled manufacturing techniques have been proposed in the prior art. In known arrangements for sewing a high precision seam, relative motion between the fabric-to-be-joined to the stitch forming mechanism is established (as in U.S. Pat. Nos. 4,457,243, 4,632,046 and 4,512,269, for example). The facility with which position control is achieved is a key factor in producing a quality seam of desired seam trajectory without involvement of human operators.
Accordingly, it is an object of the invention to provide an improved method and apparatus for positioning and guiding sheet material, e.g., fabric or other limp material to be processed.
It is another object of the present invention to provide an improved flat-material manipulation device suitable for automatic or computer-controlled manufacturing operations, which is of simple, rugged, versatile, and economical design.
Yet another object of the present invention is to provide an improved method and apparatus for precision feeding of fabric-to-be-joined at a sewing station.